For several tens of years, polyester, in particular polyethylene terephthalate (PET) has been increasingly used in the production of hollow containers, in particular bottles.
Commercial PET (called hereafter oil-PET) is generally produced with diacid and diol monomers synthesized with petrochemically-derived raw material (raw materials obtained from petrochemistry). Because of decline of world oil reserve and increasing oil prices, and/or because of the need to improve the carbon footprint of materials, many researches have been made for completely or partially replacing petrochemically-derived raw material by raw material coming from biologically based materials (bio-materials).
A polyester made from bio-materials has already been proposed. This polyester is polylactic polyester (PLA) and is made with lactic acid as acid monomer. Lactic acid is produced from bio-materials like rice, corn, sugars, etc.
However, PLA cannot replace PET in all applications due to the different properties of PLA and PET. For example, PLA cannot be used to produce containers for carbonated beverages due to the lower gas barrier property of PLA.
Consequently, investigations have been done for providing a method for producing PET from monomers obtained at least partially from bio-materials, hereafter called bio-PET.
WO 2009/120457 provides a bio-PET. This bio-PET comprises 25 to 75 wt. % of terephthalate compound selected from terephthalic acid, dimethyl terephthalate, isophthalic acid, and a combination thereof. It also comprises 20 to 50 wt. % of diol compound selected from ethylene glycol, cyclohexane dimethanol, and a combination thereof. At least 1 wt. % of the terephthalate compound and/or the diol compound is obtained from bio-materials. The bio-PET of WO 2009/120457 can be used for manufacturing beverage containers. The bio-PET of WO 2009/120457 can be differentiated from an oil-PET with a method using 14C (carbon-14) detection.
Indeed, it is known that 14C, which has a half-life of 5,700 years, is found in bio-materials but not in raw material coming from petrochemical industry. The amount of 14C can be determined by measuring the number of disintegrations per minute per gram carbon value (dpm/gC) reflecting the decay process of 14C. Such a measurement is possible through liquid scintillation counting.
Thus, a PET beverage container having a high 14C content is a PET beverage container made at least partly from bio-PET, whereas a PET beverage container having a tow 14C content is a PET beverage container totally made from oil-PET. The amount of bio-material can be simply evaluated by using 14C measurements, for example according to method ASTM D6866-10.
Although the bio-PET described in WO 2009/120457 erroneously lists isophtatic acid as a terephtalate compound, it does not disclose it as a compound that can be used as a crystallization retarding compound. It does not disclose the amount of crystallization retarding compound that should be used to obtain a bio-PET that is sufficiently clear (spherulitic crystallization can occur and decrease clarity) and/or that has the needed properties for packaging elements such as beverage containing bottles. There is need for methods to prepare bio-PET materials and packaging elements, such as bottles, that allow a bio-PET that provide a bio-PET that sufficiently clear and/or that has the needed properties for packaging elements such as beverage containing bottles.